I've read/seen a lot about how the US Gov apparently fabricated 9/11.. I doubt we'll ever know the truth.
Zadok's right, we'll probably never know the truth, but what I think is interesting is the fact (as like the JFK assasination) there is evidence that hasnt't been released - the camera footage they mention at the end. seems like the FBI are covering up something
If you find that interesting and have some time set aside, this website features a full documentary on the conspiracy. http://www.loosechange911.com/ It's one of the only conspiracies I actually believe.